// 4. 输入年份和月份，显示该年当月的天数。
var year = 2000 //年份
month = 1 //月份var
var day = 0 // 天数

switch (month) {
	case 1:
	case 3:
	case 5:
	case 7:
	case 8:
	case 10:
	case 12:
		day = 31
		break
	case 4:
	case 6:
	case 9:
	case 11:
		day = 30
		break
	case 2:
		if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
			day = 28
		} else {
			day = 29
		}
        break;
}
console.log(year+'年是'+day);
